1. Field of the Invention
The present general inventive concept relates to a conductive toner supply roller and a method of manufacturing the supply roller. More particularly, the present general inventive concept relates to a method of manufacturing a conductive toner supply roller by impregnating a polyurethane foam with a conductive impregnation solution and drying the polyurethane foam, so that a conductive polyurethane foam toner supply roller of low to medium resistance may be manufactured and may be used in an electrostatic recording apparatus such as a printer, a facsimile machine, a copier or the like.
2. Description of the Related Art
Electrostatic image forming apparatuses, such as laser printers, facsimile machines, and copiers, are provided with conductive toner supply rollers. FIG. 1 illustrates the structure of a conventional laser printer 10 as an example of an image forming apparatus.
Referring to FIG. 1, a charger 11 of the laser printer 10 electrifies a photosensitive medium 12. An electrostatic latent image is formed on a surface of the photosensitive medium 12 by a light projected by a laser scanning unit 13. The electrostatic latent image is developed by a developing roller 14 into a toner image using toner T supplied by a toner supply roller 15. The toner image is transferred onto a paper P by a transfer roller 16 and then fixed by an image fixing device 17. The toner supply roller 15 is an essential part of a developing device, as it supplies the toner T to the developing roller 14 and recovers remaining toner not used for the development of the electrostatic latent image by the developing roller 14. The toner supply roller 15 keeps the toner at a constant charge per mass (Q/M) in association with the developing roller 14 or a control blade 18.
FIG. 2 illustrates the toner supply roller 15 of the laser printer 10 of FIG. 1. In FIG. 2, the toner supply roller 15 includes a shaft 15a and a resilient member 15b enclosing an outer circumference of the shaft 15a. The resilient member 15b of the toner supply roller 15 is usually made of a polyurethane foam or a silicone foam. The polyurethane foam has a lower hardness than the silicon foam. Since the polyurethane foam has relatively low hardness and low toner stress and accordingly improves a lifespan of the toner supply roller 15, it is suitable for use in a high-speed image forming apparatus. The toner supply roller 15 including the resilient member 15b made of the polyurethane foam is capable of controlling the toner supply and toner electrification according to the raw material of the polyurethane, cell size, hardness, percentage of closed cells, and density of the polyurethane foam.
Conventionally, an ionic conductive agent or an electroconductive agent is added to the foam, to electrify the polyurethane foam constituting the resilient member 15b of the toner supply roller 15. However, since a blowing agent may become sticky or collapse when the ionic conductive agent is used in large quantities, for example when an amount of 10 parts per hundred rubber (phr) or greater is used, the ionic conductive agent should be added in a small amount. Accordingly, it is difficult to provide a polyurethane foam having a resistance of a medium or low degree (for example, 1.0E+08 or less) to the blowing agent. Such an ionic conductive type is used with a resistance equal to or greater than 1.0E+08. An electroconductive type agent means that a carbon black is added together with polyol and isocyanate. However, when a carbon black having a small average particle diameter and a high resistance is added, the polyurethane foam gets sticky. Therefore, formation of the blowing agent becomes difficult, and it is hard to make a cell arrangement even.
Moreover, in a case of impregnating the polyurethane foam with an impregnation solution containing a carbon black, a binder resin and a solvent to electrify the polyurethane foam, it is difficult to implement a polyurethane foam having a low or medium resistance (1.0E+05 to 1.0E+07). The polyurethane foam has a low resistance, that is, a resistance less than or equal to approximately 1.0E+05, thereby causing current to leak, an inferior supply of toner and a decrease in the density.